1. Field of the Invention
The present invention relates to a method for manufacturing an integrated wheel for a vehicle, on which a tire is mounted, by a combination of billet die-forging press spreading and rotative ironing.
2. Description of the Prior Art
A method for manufacturing an integrated wheel for a vehicle, on which a tire is mounted, is disclosed in Japanese Patent Publication No. 26941/80.
This prior art will be briefly described with reference to FIG. 4 (1), (2), (3) and (4). FIG. 4 (1) shows a forged article 4 comprising a disc 1, a thick flange 2 and a thin flange 3, the article 4 being normally molded by three repetitions of die forging.
Then, the forged article 4 is set to a mold 5 shown in FIG. 4 (2), and the thick flange 2 is drawn axially and outwardly by rotative ironing. Thereafter the drawn portion 7 is spread outwardly by means of a press mold 6 as shown in FIG. 4 (3), after which it is placed in a finishing mold as shown in FIG. 4 (4) for processing by a finishing roller 9.
The aforementioned prior art has the following problems despite its merits.
Since the forged article 4 is processed so as to have the thin flange portion 3 corresponding to approximately the shape of a rim, there are involved problems in that at least three repetitions of die forging steps are required so as to thus increase the number of steps, and thus several kinds of molds having a complicated shape are required, many accessory work steps such as dismantling of the mold have to be made, and a higher production cost is involved.
Moreover, in the drawing step, material is caused to move in a drawing direction by the drawing step, and therefore the machining efficiency is deteriorated and the number of machinings increases, resulting in a reduction in service life of tools and in unevenness in the shape of products even if the latter are subjected to finishing.